The present invention relates to a submersible watercraft; in particular, to a submersible watercraft having two hulls disposed generally parallel to and spaced apart from each other. At least two towers or columns are disposed generally above the hulls approximately in a longitudinal symmetry plane. The two hulls and the columns are rigidly interconnected a support surface. The towers or columns can contain propulsion and control mechanisms, crew accommodation and other equipment, such as ROV""s, diver work chambers, pipeline repair gear or other operating equipment.
Experience with oil and natural-gas exploration, production and transmission in the North Sea has shown that, because of the frequent bad weather, surface vessels can have difficulty in moving a rig or platform from the shore to an offshore location. Considerable time can be spent waiting out the storms for calm water, which is important when transporting a heavy device, such as a platform. This waiting causes a major loss of working time for surface vessels engaged in any North Sea project or project where turbulence of the water is an issue.
Moving a large platform in pieces is also expensive and time consuming, as construction now must be performed at sea, in less than stable working conditions. The present invention was developed to enable the transport of rigs and drilling platforms even in rough sea conditions by submerging to one of two levels, while retaining the option to operate in a normal draft.
German Offenlegungsschrift 23 56 537 discloses a catamaran surface vessel having a submersible gondola located between the two hulls of the catamaran. The catamaran remains afloat when the gondola is lowered for underwater travel. The submersible gondola has a torpedo-like shape widely used for self-propelled underwater craft because of its low resistance to motion for the volume of water displaced, relative to other shapes. Although the catamaran, by virtue of the form stability provided by its two spaced-apart hulls, has a high resistance to capsizing, it is nonetheless susceptible to bad weather and rough seas as are other surface vessels. U.S. Pat. No. 1,757,174 to Douglas discloses a seagoing vessel having five pontoons: a cabin pontoon, two waterline pontoons, and two power pontoons. The two waterline pontoons are disposed below and to either side of the cabin pontoon. A power pontoon is disposed below each waterline pontoon. The vessel of U.S. Pat. No. 1,757,174 is a surface vessel. Only the power pontoons, located beneath the waterline pontoons, are submerged when the vessel is under way. Consequently, the vessel is also affected by heavy seas.
A need has existed for vessels, which can have substantially the body of the vessel, submerged and still move through the water.
A submersible catamaran having a bow and a stern further comprising: a first submergible float comprising a first float rounded triangular bow, a first float midsection, a first float tail, and first float stern; a second submergible float comprising a second float rounded triangular bow, second float midsection, second float tail, and second float stern, wherein the second submergible float is disposed in a parallel relation to the first submergible float; a solid support surface forming a top to the first and second submergible floats and wherein the solid support surface is adapted for supporting heavy loads and forming an air gap between the first and second submergible floats and the solid support surface and a slot opening disposed between first and second submergible float tails; a first load supporting movable column disposed on the solid support surface; a second load supporting movable column disposed on the solid support surface; a first fixed column disposed on the first submergible float; a second fixed column disposed on the second submergible float; a first ballast system disposed in the first submergible float; a second ballast system disposed the second submergible float, wherein the first and second ballast systems are adapted to raise and lower the catamaran with respect to the waterline; a horizontal positioning system comprising: at least three horizontal maneuvering winches; at least three maneuvering lines, each connected on one end to a winch and on the other end to an horizontal maneuvering object at sea; and a controller for orienting the catamaran relative to the object at sea, and wherein the controller monitors the tension on the maneuvering lines and the controller initiates winch pay out of the maneuvering line when load on any one of the maneuvering lines exceeds a first preset limit, and further the controller initiates the maneuvering winch tensioning of the maneuvering line when tension on any one of the maneuvering lines falls below a second preset limit; and a vertical positioning system for securing the catamaran to an object at sea; a first line secured on one end substantially vertically to an object at sea; a second line secured on one end substantially vertically to the object at sea; a first motion compensation system disposed in the first load supporting moveable column and connected to the other end of the first line; a second motion compensation system disposed in the second load supporting moveable column and connected to the other end of the second line; and a control system for monitoring and controlling tension between first and second motion compensation system and the object at sea.